Inotrope-dependent patients may become haemodynamically unstable during treatment in the hyperbaric chamber. One possible cause is altered performance of infusion devices. We tested six Atom 235 syringe infusion pumps under hyperbaric conditions of 2.8 atmospheres absolute in a multiplace chamber using a gravimetric method. There was a small but significant reduction in infused volume during a thirty-minute period including compression time. We concluded that altered inotrope delivery may explain at least some of the haemodynamic instability sometimes seen, although a physiologic effect of hyperbaric treatment cannot be excluded.